Noise reducing system



NOV. 5, 1940. M 2,220,165

NOISE REDUCING SYSTEM Filed June l'7, 1936 l g h FiG-I. 26 2? 2a 2.9 a0

RECEIVER I. F! OUTPUT r' g I aez/van 2, 6-?- ou'rPu'r 12 40 Q i v zlvvalv'ran a Louie; Malter Patented Nov. 5, 1940 PATENT OFFICE 2,220,165 NOISE REDUCING SYSTEM Louis Malter, Oaklyn,

Corporation of America,

ware

N. J., assignor to Radio a corporation of Dela- Application June 17, 1936, Serial No. 85,662

8 Claims. (01. 250-20) This invention relates to the reduction of the noise likely to be produced in radio receivers and similar apparatus by electrical impulses extraneous to the signal impulses. It has for its principal object the provision of an improved apparatus and method of operation whereby the signal channel transmitting efficiency is controlled in a manner to preclude .the passage of vice 22 provided with impulses likely to produce noise. In particular, the invention involves the use of an electron gun or similar device which functions in response to impulses of relatively high amplitude to change the conductivity of the signal channel for the duration of such impulses.

The invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope is indicated by the appended claims.

Referring to the drawing: 1

Fig. 1 illustrates the application of the invention to an intermediate stage of a radio receiver,

1A shows a detail of a portion of a tube of Fig. 1, and

Fig. 2 illustrates the invention as applied to an audio stage of such a receiver.

The system of Fig. l and Fig. 1A includes an antenna Ii], or other suitable signal pick-up device, from which signal impulses are supplied to an output circuit II through a signal channel including a radio receiver l2, a transformer l3, an intermediate frequency stage I4 and a transformer 15. Connected between the cathode l6 and the control grid [1 is a capacitor I8 which is shunted by a resistor It] provided for the purpose of controlling the grid bias potential of the amplifier 14 in response to impulses of relatively high amplitude.

Control of the amplifier grid bias potential in this manner is effected through a control, channel including an amplifier 20 shunted by a resistor 2| and an electron gun or cathode ray dedefiecting electrodes 23 connected to the output terminals of the amplifier 20. In order to produce a circularly shaped electron beam, the gun 22 is preferably provided with another pair of deflecting elec trodes (not shown) which are connected substantially perpendicular to those illustrated and are connected respectively to the leads 25. The gun 22 includes a cathode 26, a grid 21, anodes 28 target electrode 3| which is preferably of circular shape and an outlet electrode target 32 which is preferably of annular shape and surrounds but is spaced from the circular target 3|, as shown more fully in Fig. 1A.

It will be noted that (1) batteries 33 and 34 are connected between the cathode 26 and the target 3|, (2) the resistor 19 is connected be- 24 and r and 29, an electrode auxiliary 30, a.

Fig. l in most that it includes a detector 60 and the noise tween the target 32 and the high, voltage terminal of. the battery 34, (3) the electrode 30 is connected through a battery 35 and a reversing switch 36 to the high voltage terminal of the battery 34 and (4) the resistor I9 is shunted by a capacitor 31 and is connected through a reversing switch 38 to the input circuit of the amplifier I4.

Operation of the system of Fig. 1 and Fig; 1A is based on the fact that the deflecting electrodes 23 are subjected to, a signal potential of such amplitude that the circularly shaped electron beam of. the gun 22 extends to the periphery of the target 3! when the signal carrier present in the output of the amplifier 20 is about one hundred per cent modulated. Under this conclition, no current is supplied from the gun 22 through the resistor i9 to bias the input circuit of the amplifier M and this amplifier is unaffected by the output current of the gun. When the level of the signal, at one hundred percent modulation, is exceeded by impulses of relatively high amplitude, however, the periphery of the electron beam extends to the surface of the annularly shaped electrode 32, current flows through the resistor 19 and subjected to a noise suppressing negative bias potential which prevents the passage of the rela-- tively high amplitude impulses to the output terminals ll.

The target output electrode 32 may or may not be provided with an electron emissive coating. If it is not provided with an emissive coating the operating positions of the switches 36 and 38 are as illustrated, and the electrode 38 is connected to the negative terminal of the battery 35 and the gun functions with primary electrons derived from the cathode 26 to produce a negative grid bias drop in the resistor l9. If it is provided with such a coating, the switches 36 and 38 are moved to their other closed positions, and the electrode 36 is connected to the positive terminal of the battery, secondary electrons flow from the target 32 through the electrode 30 and the battery 35 to the resistor l9, and the input circuit of the amplifier M is biased as previously indicated. Operation with secondary emission has the advantage that the outputof the gun may be amplified to an extent depending on the character of the emissive coating, a four fold amplification being readily 0btainable and an eight fold amplification being possible. I

The system of Fig. 2 is similar to that of respects but differs therefrom in suppressing bias potential derived from the gun 22 is applied to the input circuit of a pushpull audio frequency stage M. The operation of this system and the application of an electron the amplifier input circuit is provided with input and output circuits, an impedance device connected in said input circuit, a cathode ray device providedwith output electrodes comprising an inner circular targetand an outer annular target closely spaced therefrom, said electrodes being connected respectively with the opposite ends of said impedance device, and meansresponsive to radio frequency impulses in said channel above a predetermined level for shiftingsaidray from one to the other of said output electrodes, and for maintaining said ray on said one output electrode in response to signals having a normal. amplitude level.

2. The combination of a modulated signal channel includingan electric discharge device provided with input and output circuits, an impedance device connected in said input circuit, a cathode ray device provided with an auxiliary electrode, a circular target electrode, and an annular output electrode located adjacent to and surrounding the target electrode, said target and output electrodes being connected respectively with the opposite ends of said impedance device, means responsive toimpulses in said channel above a predetermined level for shifting the cathode ray of said device from the target electrode to the output electrode, and means'connected between said auxiliary electrode and said impedance device for causing current dependent the primary electrons to be transmitted through on the primary electrons of said cathode ray device tobe transmitted through said impedance device,

3. The combination as defined in claim 2 further characterized by the fact that the connection between the impedance device and the input circult is provided with switch means for reversing the polarity of the connection, and that the lastnamed means for causing current dependent on the said impedance device includes a switch for applying a more positive potential to said auxiliary electrode, and an electron on-said output electrode. I 4. The combination of a modulated signal channel including radio and audio frequency amplifyemissive' coating ing stages, an electron gun having means for producing a circular electron beam, means responsive to signals from said radio frequency stage for causing said gun to provide a deflection of the beam, substantially coplanar annular target electrodes for receiving said beam, means for adjusting the amplitude ofsaid signals to effect a deflection of said beam into the outer annular target electrode in response t'ogimpulses of an amplitude exceeding a predetermined value corresponding substantially to a level of signals at substantially modulation, and means connectedwith said outer electrode for suppressing the output of said audio frequency amplifier when said beam is so deflected. c c

5. In a modulated signal amplifying channel, the combination of an electric discharge amplifier device provided with input and output circuits, an impedance device connected in said input circuit,

1 of said impedance device and. both the cathode and the inner circular target electrode, means responsive to signals applied to said input circuit for maintaining the cathode ray of said cathode ray device on the inner circular target electrode in response to signals having a predetermined maximum amplitude, said last means including an additional amplifier interposed between said input circuit and said cathode ray device, and means for adjusting said last named means for causing said I cathode ray to shift from the inner circular target electrode to the outer annular target electrode in response to electrical impulses having an amplitude higher than said maximum value.

6. The method of limiting the amplitude of impulses in a signal channel having a thermionic amplifier and an impedance device connected to a control electrode thereof, by means of a vacuum tube device having a cathode, anode, control electrode and a plurality of other electrode elements, which comprises so adjusting exterior circuit values affecting said tube that at least a major portion of the current through said cathode deriving from the electron stream passes through elements in said tube other than said anode when the input signal voltage is greater than a predetermined value, and suppressing the output of said amplifier by causing the electron current passing through said other electrode elements to actuate said impedance device and thereby to set up a bias potential on said control electrode of said amplifier,

' 7. The method of limiting the amplitude of radio frequency impulses in a signal channel ineluding a radio frequency amplifier by means of a cathode ray tube having a cathode, a target electrode and an output electrode, and deflecting means, which comprises so adjusting exterior circuit values affecting said cathode ray tube that the cathode ray impinges upon said target electrode for effecting normal signal transmission in said channel, and causing at least a major portion of said ray to be deflected from said target electrode to said output electrode in response to radio frequency impulses above a predetermined level, and causing thereby a reduction in the output of said radio frequency amplifier for the duration of said impulses.

8. The combination in a signal channel including a pair of electric discharge devices having grids, anodes and cathodes, connected in pushpull relation, input and output coupling devices connected respectively to said grids and anodes, an impedance element connected between said cathodes and a low potential point on the input coupling device, a cathode ray device having a target electrode and an output electrode connected to said impedance device, and means responsive to electrical impulses in said channel above a predetermined level for shifting said ray from said target electrode to said output electrode in response to impulses above a predetermined signal level foreffecting a voltage drop through said impedance device to suppress the output of said push-pull connected discharge devices for the duration of said impulses.

V l LOUIS MALTER. 

